Pallas traveled throughout the Netherlands and to London, improving his medical and surgical knowledge. He then settled at The Hague, and his new system of animal classification was praised by Georges Cuvier. Pallas wrote Miscellanea Zoologica (1766), which included descriptions of several vertebrates new to science which he had discovered in the Dutch museum collections. A planned voyage to southern Africa and the East Indies fell through when his father recalled him to Berlin. There, he began work on his Spicilegia Zoologica (1767–80).

Title of the book Journey through various provinces of the Russian Empire

Pallas settled in St Petersburg, becoming a favourite of Catherine II and teaching natural history to the Grand Dukes Alexander and Constantine. He was provided with the plants collected by other naturalists to compile the Flora Rossica (1784–1815), a Russian flora, and started work on his Zoographica Rosso-Asiatica (1811–31), a zoography of Russia and Asia. He also published an account of Johann Anton Güldenstädt's travels in the Caucasus. The Empress bought Pallas's large natural history collection for 2,000 rubles, 500 more than his asking price, and allowed him to keep them for life. During this period, Pallas helped plan the Mulovsky expedition, which was cancelled in October 1787.

Between 1793 and 1794, Pallas led a second expedition to southern Russia, visiting the Crimea and the Black Sea. He was accompanied by his daughter (by his first wife who had died in 1782) and his new wife, an artist, servants, and a military escort. In February 1793, they travelled to Saratov and then downriver to Tsaritsyn. They spent the spring exploring the country to the east, and in August travelled along the banks of the Caspian Sea and into the Caucasus Mountains. In September, they travelled to the Crimea, wintering in Simferol. Pallas spent the spring of 1794 exploring to the southeast, and in July travelled up the valley of the Dnieper, arriving back in St Petersburg in September. Pallas gave his account of the journey in his P. S. Pallas Bemerkungen auf einer Reise in die Südlichen Statthalterschaften des Russischen Reichs (1799–1801). Catherine II gave him a large estate at Simferopol, where Pallas lived until the death of his second wife in 1810. He was then granted permission to leave Russia by Emperor Alexander, and returned to Berlin, where he died in the following year. His grave is preserved in the ProtestantFriedhof I der Jerusalems- und Neuen Kirchengemeinde (Cemetery No. I of the congregations of Jerusalem's Church and New Church) in Berlin-Kreuzberg, south of Hallesches Tor.

Pallasite

In 1772, Pallas was shown a 680-kg lump of metal which had been found near the city of Krasnoyarsk. Pallas arranged for it to be transported to St Petersburg. Subsequent analysis of the metal showed it to be a new type of stony-iron meteorite. This new type of meteorite was called pallasite after him, whereas the meteorite itself is named Krasnojarsk or sometimes also called Pallas Iron (the name given to it by Ernst Chladni in 1794).